In a large saucepan, melt butter over a medium heat. Add the onions and leeks and sweat for 10 minutes, until the mixture just starts to brown. Add the garlic and cook for a further two minutes. Add the Agria potatoes, Simon Gault Home Cuisine vegetable stock and simmer for 30 minutes until the potatoes are tender. Remove from the heat and blend with a food processor or stick blender until smooth. Return to the pot, add Simon Gault Home Cuisine Kiwi seasoning and cream and bring back to a simmer. Serve with a quenelle of crème fraiche and freshly chopped chives.